Yes, coos is a Scrabble word!
...and is worth 6 points in Scrabble, and 7 points in Words with Friends
coos
Verb
1. Speak softly or lovingly
2. Cry softly, as of pigeons
Noun
1. The sound made by a pigeon
What Scrabble words can I make with the letters in coos?
3 Letter Words
2 Letter Words